In coal burning boilers of the type used in steam production for energizing electrical generating systems, it is a requirement that flyash be removed from the gas to reduce atmosphere contamination to a controlled minimum.
This is accomplished in part by the provision, between the boiler outlet and the stack, of a precipitator, whose function is to collect flyash from the exhaust and drop it into hoppers for subsequent disposal.
As commonly used today, these precipitators comprise hundreds of vertical, closely spaced wires, suspended from energized bars which maintain the wires at a high d-c voltage (ca 50000 v). The individual wires have laterally restrained weights at their lower ends to maintain them under tension in separated vertical relationship.
In a commercial installation to which the improvement of the present invention is applied, the weights attached to the lower ends of the individual wires are of bottle shape with reduced necks at their tops. Stop washers are applied to the tops of the reduced necks, and extend radially beyond the necks. Eyebolt guides for each weight provides a ring surrounding the neck through which the washer cannot pass. Accordingly, when a wire fails, the weight is prevented from falling into the hopper.
In practice the wires are about 30 feet long, one hundred mils (0.100") in diameter, with foot long 3/8" diameter rods at both ends, formed to hook shape to suspend the wire from an energized support and to suspend the weight at the bottom of the wire. Weights of approximately 16 pounds are used. The wires are arranged in rows between grounded vertical plate which define passages between adjacent plates for flow of products of combustion.
The basic problem with these precipitators has been that broken wires within a section between adjacent plates cause the plates to be short circuited, and requires that the shorted section must be de-energized. The loss of each section reduces collection efficiency, necessitating reducing the load to stay within stack emission limits. Eventually enough sections are shut down to force an outage for maintenance (removal of shorted wires and replacement thereof).
Wire failure cannot be avoided and may be due to corrosion, erosion, arcing or fatigue.
In accordance with the present invention, an arrangement is provided which will cause automatic removal of both portions of a failed wire, so that each section may stay in operation so long as enough wires remain in service to maintain stack emission within required limits.
Specifically, this is accomplished by providing each wire with suspension means which is maintained in operation by the weight of the wire and its attached weight. A simple embodiment of the invention is one in which a weighted pivotable support is employed, including a hook movable to release position when the load of the wire and its weight is removed.